In order to produce fluid from a well, artificial lift systems may be used, for example, using a rotating drive shaft to drive a pump. In an oil and gas well, progressive cavity pumps are often used to assist in the production of hydrocarbons from subterranean formations. At a well site, a progressive cavity pump is driven from the surface using an engine or motor which drives a drive shaft that drives the downhole pump.
It is important for the drive mechanism to include a braking system to slow the rotation of the drive shaft in a reverse direction. During production, various factors can cause the drive shaft to begin rotating in a reverse direction. Pump failure, for example, caused by failure of the drive mechanism, may cause built up production fluid in the production string to fall back into the well, causing the progressive cavity pump to be driven in reverse. Due to the length of the drive shaft, torque may also build up in the drive shaft during operation of the pump, which, when released, may also cause rotation in the reverse direction at the surface. Failure to control the resulting backspin may have catastrophic consequences at the top of the well, including damage to surface equipment, including the drive mechanism itself, and increase the risk of injuries to workers at the surface.
Various attempts to control the backspin of drive shafts have been disclosed in the art.
Canadian Patent Application No. 2,831,233 describes a centrifugal backspin brake which uses a spring and a counterweight to drive brake shoes to engage a brake drum.
Canadian Patent No. 2,322,656 describes a centrifugal backspin retarder having a brake actuator and a stationary brake member. The brake actuator retains the brake shoes in their retracted positions during forward rotation and urges the brake shoes into more intimate contact with the stationary brake member during reverse rotation of the shaft by applying an additional radial outward force against the brake shoes.
Canadian Patent No. 2,350,047 describes a centrifugal brake assembly that includes a driving hub and a driven hub that have adjacent surfaces with respective grooves for receiving drive balls. The adjacent surfaces each lie in a plane that is perpendicular to the axis of rotation to the drive shaft. Brake shoes are connected to the driven hub. A helical tension spring on each of the brake shoes biases the brake inwardly toward respective non-braking positions.
Previous designs which use a ball and groove design have been known to occasionally hydroplane or skip, especially in colder temperatures, resulting in a failure of the brake to engage. Cold temperatures may affect the ability of such devices to function properly due to increases in fluid viscosities at those temperatures. Given the destructive and potentially dangerous consequences of uncontrolled backspin, there is a need for a backspin device that overcomes at least some of the disadvantages of prior brake designs.